What Does P20C3 Mean?
The PCM has detected a voltage signal lower than expected in the control circuit for reductant heater C. This heater is part of the diesel exhaust fluid (DEF) system that prevents freezing and ensures proper SCR operation.
Common Causes
35%
Short to ground in heater control circuit wiring
30%
Faulty reductant heater C element
20%
Failed reductant control module or driver circuit
15%
Corroded or damaged connector at heater C
Diagnostic Steps
1
Step 1: Inspect reductant heater C connector for corrosion, damage, or moisture intrusion
2
Step 2: Measure resistance of heater C element (typically 0.5-3 ohms when cold) and compare to specifications
3
Step 3: Check for continuity and short to ground in control circuit wiring from module to heater
4
Step 4: Test voltage supply at heater connector with key on (should see battery voltage when commanded on)
5
Step 5: If wiring and heater test good, suspect reductant control module driver circuit failure
Estimated Repair Cost
$200 - $800
Parts + labor, varies by vehicle and location
The PCM has detected a voltage signal lower than expected in the control circuit for reductant heater C. This heater is part of the diesel exhaust fluid (DEF) system that prevents freezing and ensures proper SCR operation.
The most common cause of P20C3 (Reductant Heater "C" Control Circuit Low) is: Short to ground in heater control circuit wiring
Typical repair costs for P20C3 range from $200 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive but may enter reduced power mode. Extended operation may damage SCR catalyst and lead to NOx emissions non-compliance.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P20C3 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Emissions System (SCR/DEF)
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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